In a conventional ink jet printer, ink is deposited on record media such as paper via a disposable pen, the pen being mounted on a carriage for reciprocation across the paper's face. Ink is ejected through the pen's printhead, the printhead being connected to a volume of ink which is stored in a reservoir onboard the pen. When the ink reservoir is depleted, the pen is removed from the carriage, discarded, and replaced with a new pen. An example of such a pen is disclosed in U.S. Pat. No. 4,771,295, which is entitled "Thermal Ink Jet Pen Body Construction Having Improved Ink Storage and Feed Capability", and which is commonly owned herewith. The disclosure of that patent is incorporated herein by this reference.
In order to extend the useful life of ink jet pens, several off-axis ink supply approaches have been suggested whereby the pen's onboard ink reservoir is refilled. These approaches have included the use of a second, off-board ink supply, generally in the form of a larger ink reservoir positioned at a location which is remote from the pen. As the pen's onboard supply of ink is depleted, substitute ink is delivered from the off-board reservoir through an arrangement of one or more tubes. The larger ink reservoir thus allows for use of the pen beyond the duration of the its onboard ink supply, effectively extending the pen's lifetime to coincide with the lifetime of the its associated printhead. An illustrative example of such an approach is provided in U.S. Pat. No. 4,831,389, which is entitled "Off Board Ink Supply System and Process for Operating an Ink Jet Printer", and which is commonly owned herewith. The disclosure of that patent is incorporated herein by this reference.
Although known off-axis ink supply approaches generally have been effective in extending the lifetime of a printer's pen, there remains room for improvement, particularly in the manner by which ink is delivered to the pen. In the past, ink has been delivered via flexible tubing which runs from the off-board ink supply to the reservoir within the pen. The tubing generally extends as a linear segment, each tube having a length which allows for reciprocation of the pen. As the pen reciprocates, and the distance between the pen and off-board reservoir changes, the tubing is folded over on itself so as to take up the resulting slack.
This tubing arrangement has led to a number of problems, due in large part, to the effects of tube folding during reciprocation of the pen. Such folding, for example, will often produce an unacceptably high stress on the tube, increasing tube fatigue, and correspondingly decreasing the lifetime of the tube. In addition, folding of the tubes may result in an undesirably high torque on the pen, increasing the power required to drive the pen. Further, because the folding of tubes requires a significant amount of clearance, the use of off-axis ink supplies has resulted in a significant increase in the printer's size. The latter problem is particularly troublesome where a multi-color pen is employed, it being necessary to run a plurality of tubes (one for each color) between the reservoir and the reciprocating pen.
It is therefore a general object of this invention to provide a fluid delivery system whereby fluid may be delivered from a stationary reservoir to a reciprocating discharge mechanism without the stress caused by folding or extreme bending of tubes. More specifically, the invention is intended to provide an off-axis fluid delivery system wherein tubes are formed helically so as to allow expansion and retraction of the tubes without imposing undue stress or fatigue.
Another general object of the invention is to provide an off-axis fluid delivery system which employs tubes to deliver fluid from a stationary reservoir to a discharge mechanism without unduly burdening discharge mechanism reciprocation. This relates most directly to the minimization of torque on the discharge mechanism by the tubes, such minimization being made possible by effecting a decrease in the drag produced by the tubes. It is therefore an object of the invention to provide a fluid delivery system which delivers fluid through tubes formed in spring-like coils.
Yet another general object of the invention is to provide an off-axis fluid delivery system with multiple tubes which optimizes the space such tubes occupy. Specifically, it is intended to provide a fluid delivery system which interconnects a stationary reservoir and a reciprocating discharge mechanism via a plurality of concentrically coiled tubes.